Count objects with the camera

Parts in this circuit

Wiring, pin by pin

Red = 5 V, orange = 3.3 V, black = GND, other colours = signals. “Pin” is the position on the 40-pin header; the GPIO number is what the code uses. Power the Pi from a 5.1 V supply and wire with the power off.

Python code (gpiozero)

from picamera2 import Picamera2
from gpiozero import LEDBarGraph
from time import sleep

cam = Picamera2()
cam.configure(cam.create_preview_configuration())
cam.start()
sleep(1)

bar = LEDBarGraph(17, 27, 22, 23, 24)
count = 0
was_left = None                       # where the ball was last time

while True:
    frame = cam.capture_array()
    spot = frame.find_color("red")
    if spot is None:
        was_left = None               # nothing to follow
    else:
        left = spot[0] < frame.width / 2
        if was_left is True and not left:
            count += 1                # it crossed the middle line, left to right
            bar.value = min(count, 5) / 5
            print("Count:", count)
        was_left = left
    sleep(0.1)

How the code works

• was_left remembers on which side of the middle line the ball was in the last picture.
• A count happens only when it changes from left to right. A ball that stays on one side counts once at most.
• Setting was_left to None when nothing is seen stops false counts when a new ball appears.
• bar.value = count / 5 lights that fraction of the LEDs.

Parts to buy

The links open a search on each store, so you see what is in stock today. Check the model, voltage and price before you order.